UC San Diego

While stress is known to suppress reproductive activity, the underlying mechanism has not been fully elucidated. Because stress is associated with elevated corticosterone levels in mice, we investigated corticosterone’s potential role in inhibiting the reproductive neuroendocrine axis. Three experiments were performed in vivo using gonadectomized male mice. First, with corticosterone injections in C57Bl6 mice, we observed neuronal activation of dorsal-medial hypothalamic RFamide-related peptide 3 cells (RFRP-3, the mammalian ortholog of Gonadotropin Inhibiting Hormone) via double-label in-situ hybridization (ISH). We found that Rfrp and cfos mRNA co-expression significantly increased 30 minutes post-injection, which is also when corticosterone levels are at their highest (measured via ELISA). Because of this relationship between corticosterone and RFRP-3 neuronal activation, we conducted a second experiment using restraint stress in transgenic mice with glucocorticoid receptors (GR) knocked out of only RFRP-3 neurons. Corticosterone is known to bind to GR. With an ultra-sensitive murine LH ELISA, we found that LH pulses were inhibited even when GR was knocked out, suggesting that GR presence in RFRP-3 cells is not needed for stress-induced LH inhibition. To test whether GR presence is needed for RFRP-3 neuronal activation during stress, we utilized 45- and 180-minute restraint periods with the same transgenic line. Our ISH results indicated that GR absence did not change the expected increase in RFRP-3 neural activation after 45 minutes of restraint. All three experiments demonstrate that corticosterone is capable of activating RFRP-3 neurons, though stress-induced inhibition of the HPG axis does not depend on this relationship.